Insulated conductor



Sept. 25, 1928. 1,685,386

R. R. WILLIAMS INSULATED CONDUCTOR Filed May 5, 1924 Patented Sept. I 25, 1928.

UNITED STATES 1,685,386 PATENT OFFICE.

ROBERT R. WILLIAMS, OF ROSELLE, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y.,.& CORPORATION OF NEW YORK.-

insumrnn Application filed May 5,

This invention relates to insulated conductors, and particularly to continuously loaded submarine conductors.

It is an object of the invention to improve the insulation of such conductors and to apply the insulation to the conductor itself in such a manner as not to deleteriously affect the conductor or the insulating material.

The use of hard rubber or semi-hard rubber n as the insulating material for submarine conductors offers important advantages because of its low conductance, low dielectric constant, and the fact that it is more rigid than soft rubber, and therefore its osmotic swelling by water absorption is more limited.

However, if the rubber compound is fashioned on the conductor and then vulcanized, there is objection due to the action of the sulphur on the conductor during the long period of heating. A further ditliculty has been experiencedin applying this insulation to a recently developed submarine conductor which is provided with a continuous loading of a new alloy, the permeability of which at low magnetizing forces is far greater than that obtained with iron. In using this alloy it is necessary to take special precautions in order to prevent the adverse effects of hydrostatic pressures to which the insulated conductors are later subjected when submerged in great depths of water. By imbedding the conductor and the loading material of such a cable in a mass of soft fluid compound, it has been found possible to distribute the mechanical strains so uniformly on all parts of the loading material that no loss of permeability or reduction in the inductance of the assem bled cable core results upon subjection of such cores to high hydrostatic pressures. A complete disclosure of this new loading material and its application to submarine cables will be found in Patent 1,586,884 to G. WV. Elmen and Patents 1,586,87a and 1,586,875 to O. E. Buckley all of which were issued on June 1,1926. By the use of a coacting of liquir bitumen placed overthe loading material and filling the interstices between the adjacent turns of the loading material and between the loading material and conductor itself, it was found possible to properly protect the material from strains when gutta percha was used as the insulating material.

However, when the gutta perchainsulation was replaced by a rubber compound difiiculty was at once ekperienced, since the layer of CONDUCTOR.

1924. Serial No. 711,043.

fluid material was found to interfere with the application of the rubber compound by the extrusion process. This was due to the fact that the rubber compound, being less plastic than gutta percha and its adherence to the conductor being negligible because of the presence of the layer of fluid compound, could not be extruded in a layer of uniform dimensions. Under these conditions the conductor tends to slide through the insulating sheath at times so that the sheath in lagging behind is allowed to collect in lumps immediately in front of the extruding machine. Furthermore, when an insulating layer of rubber compound is applied in this manner, even with. the greatest possible degree of accuracy, another difiiculty arises during vulcanization. This difiiculty arises from the fact that the soft liquid compound suitable for imbedding the loading material fuses and mingles with the rubber compound during the vulcanization operation if this operation is carried 011 at the usual range of temperatures. By this fusion and intermingling of the rubber, the fluidity of the soft compound is so reduced that it does not satisfactorily distribute strains when the finished core is later subjected to hydrostatic pressure. F urthermore, the rubber insulating compound is softened and damaged by the mixing with the soft imbedding compound, resulting in deformation of the core and decentralization of the conductor therein.

To overcome these objections and in accordance with a feature of this invention. a separator is provided between the liquid compound and the rubber compound, this separator being composed of an insulating material which does not soften appreciably under heat or react chemically or by solution 95 upon the insulating compound or imbedding compound. It is also necessary that this separator shall not injuriously affect the electrical characteristics of the insulated conductor. Cellulose acetate has been found to 199 be a suitable separator.

In the accompanying drawing, Fig. 1 is a view of a section of cable embodying the features of this invention and Fig. 2 discloses the manner in which this conductor is 105 fabricated. In practice, the conductor itself usually consists of a central wire 5 and a plurality of conducting strands 6, 6 wound spirally thcreabout. Over this composite conductor is spirally wound the tape 7 of load- 11 ing material, which is then impregnated with and coated over with a layer of liquid bitumen 8. The separator 9 is provided over the imbedding compound 8 and separates the imbedding compound from the insulating sheath 10, which may be of rubber or similar compound. In practice, the loaded conductor is passed over suitable rollers and into a tank 11 containing the imbedding compound, which preferably consists of liquid bltumen which has a penetration of not less than 50 units in-5 seconds at 0 0. when tested by means of a penetrometer loaded with a 50 gram weight and using a standard needle of the American Society of Testing Materials. From the tank 11 the impregnated conductor passes into tank 12, which contains a bath consisting of cellulose acetate dissolved in acetone'and amyl alcohol in the following proportions: cellulose acetate 10 parts, acetone parts, amyl alcohol 20 parts. After passing through this bath of cellulose ace tate solution, the conductor passes continu ously through an oven 13, which is maintained at a constant temperature by some such means as the gas burners 14. The temperature of this oven must be determined by the rate of evaporation of the solvent from the cellulose acetate film, it being necessary that the evaporation be not too rapid in order to avoid excessive shrinkage of the residual cellulose acetate film. The imbedded conductor, after being covered with the cellulose acetate and dried, then passes into extruding tube 15 and is covered with a sheath of rubber compound in the usual manner, and then submitted to vulcanization in accordance with the well known methods. Since the cellulose acetate is inert as regards both the liquid bitumen and the rubber compound, there is no chemical action brought about by the use of this material as a separator. Its insulating characteristics are satisfactory and by preventing intermingling of the imbedding compound with the rubber compound, the

usefulness of the imbedding compound is maintained and no injury is done to the rubber compound. Furthermore, this separator prevents deleterious action of the rubber upon the conductor during the vulcanization process.

WVhat is claimed is:

1. An electrical conductor comprising a conducting core, a layer of pressure equalizing material surrounding said core, an outer sheath of insulating material, and a separator of chemically inert material positioned between said pressure equalizing material and said insulating material.

2. An electrical conductor comprising a conducting core, a layer of liquid insulating material surrounding said core, an outer sheath of solid insulating material, and a separator of cellulose acetate between the liquid and solid insulating materials.

said liquid insulating material and said outer sheath.

4. An electrical conductor comprising a conducting core, a magnetic tape wound thereabout, a layer of liquid bitumen sur rounding said tape, an outer sheath of rubber insulation, and a separator of cellulose acetate positioned between said liquid bitumen and said outer sheath.

'5. In a cable which comprises layers of fluid and solid covering materials, a separating coating between said layers for retaining the dimensional, physical and electrical characteristics of said layers.

6. A cable core comprising a conductor loaded with strain sensitive magnetic mate rial, uniform layers of fluid and solid insulating materials surrounding said conductor, and a coating of self-sustaining material completely separating said layers.

7. .A cable core comprising a conductor loaded with sensitive magnetic material, an inner layer of fluid material and an outer layer of .solid insulating material surrounding said conductor, and between said layers a separating coating of rigid material impervious to said fluid material.

8. A cable core comprising a conductor, an inner layer of fluid material about said conduct0r,'a coating of a rigid, non-porous substance enveloping said la er, and a sheath of vulcanized rubber insu ation surrounding said coating, said substance being capable of withstanding the vulcanizing process without permanent change.

9. In a method of covering a metallic core with a layer of fluid material surrounded by a layer of hard material, the step of confining said layer of fluid material within a rigid impervious envelope to prevent dimensional distortion of said layers and to eliminate physical and chemical interaction there between.

10. In a method of insulating a conductor with a covering of fluid material and then with a covering of a solid substance, the step of forming a rigid coating between said coverings to insure uniform dimensions thereof.

11. In a. method of manufacturing a continuously loaded submarine conductor which comprises coating the loaded conductor with a heavy uniform layer of fluid compound, extruding about said layer a sheath of rubber insulation and then subjecting the insulation to a \ulcanizing treatment, the step of coating said layer to protect it against deformation due to the high extruding pressures and from 11)]lll10llS ellects from chemicals and high temperatures involved in the vulcanizing treatment.

' 12. *In a manufacturing process for cover ing a conductor with a layer of .fluid and a layer of hard insulating material, the method of securing uniform dimensions of said layers comprising enveloping said layer of fluid material with a coating of cellulose acetate 'before extrudin said layer of hard material about the con uctor.

13. The method of treating a continuously loaded conductor which consists in passing said loaded conductor through a bath consisting of a normally liquid insulating material and then through a bath consisting of cellulose acetate solution, evaporating the solvent, and forming a sheath of a comparatively hardinsulating material over said cellulose acetate.

14. The; method of treating a continuously loaded conductor which-consists in passing said loaded conductor through a bath of liquid bitumen, passing the coated conductor through a solution of cellulose acetate consisting of cellulose acetate 10 parts, acetone 70 parts and amyl alcohol parts, then passing the treated conductor through an oven containingheatedair to evaporate the solvent, and extruding a-sheath of rubber about the treated conductor. A

In witness whereof, I hereunto subscribe my name this 29th day of April, A. D. 1924.

ROBERT R. WILLIAMS. 

